In situ high-pressure crystallization and compression of halogen contacts in dichloromethane.

The structure of dichloromethane, CH2Cl2, crystallized in situ in a diamond-anvil cell, has been determined by single-crystal X-ray diffraction at 1.33 and 1.63 GPa. The pressure-frozen crystal was determined to be orthorhombic, with the space group Pbcn, and isostructural with the low-temperature phase at 0.1 MPa. The CH2Cl2 molecules are located on one set of crystallographic twofold axes. The characteristics determined for the CH2Cl2 crystal (compression of the close intermolecular contacts, molecular association and the crystal habit of dichloromethane) suggest that the crystal cohesion forces are dominated by H...Cl interactions rather than by Cl...Cl attractions.